type ThumbnailDoc = {
	id: string;
	thumbnailKey?: string;
	thumbnailGeneratedAt?: string;
};

/**
 * Builds the URL for a document thumbnail image, or returns null when the document
 * has no thumbnail yet. When `thumbnailGeneratedAt` is present it is appended as a
 * `?v=…` query param so the browser / proxy cache is invalidated whenever the file
 * is replaced (the backend regenerates thumbnails at the same S3 key on replace).
 */
export function thumbnailUrl(doc: ThumbnailDoc): string | null {
	if (!doc.thumbnailKey) return null;
	const base = `/api/documents/${doc.id}/thumbnail`;
	if (!doc.thumbnailGeneratedAt) return base;
	return `${base}?v=${encodeURIComponent(doc.thumbnailGeneratedAt)}`;
}